The computer mechanisms in all 15,000 of the District's new parking meters are being sent back to the Arkansas manufacturer for adjustments after complaints by motorists that the meters sometimes fail to properly credit the coins that are deposited.

The repairs are taking place gradually, and none of the meters now earning the city $1.05 million a month has had to be taken out of service.

The trouble with the digital meters is that a device used to screen out slugs and foreign coins is also rejecting legal U.S. coins with slight flaws, said Gorm Tuxen, director of sales for Duncan Industries Inc., the meter manufacturer, based in Harrison, Ark.

"If a coin goes through that is slightly battered or bent, it won't give credit," Tuxen said. "The flaw can be so small you can't even see it."

District officials, who did not make the problems public until contacted by The Washington Post, don't know how often the meters are failing to register coins because motorists often fail to report the trouble. But in the first 11 days of June, 190 people called to report a "missed coin," according to city records. That suggests the trouble arises rarely--less than 1 percent of the time meters are used--but it is bothersome enough to prompt the fixes, city officials and the manufacturer said.

Gabriel Goldberg, a computer consultant from Alexandria, said he was parking his car recently near MCI Center when he dropped two quarters into the meter, neither of which registered. His third quarter did the trick.

"I paused and thought, 'How many quarters am I going to throw away?' " he said. "It is like an unfriendly slot machine. But I guess it is a wonderful revenue enhancer for the District."

Ann Loikow, of Cleveland Park, said she had a similar experience near George Washington University Hospital several weeks ago. Like Goldberg, she did not bother to report the problem to the city.

"I started sliding the money in there, and after putting in a couple of quarters, I noticed I only had 20 minutes of time, instead of 40 minutes," she said. "Something had not registered."

Lockheed Martin IMS, a subsidiary of Bethesda-based Lockheed Martin Corp., won a $25 million, seven-year contract last year to install and maintain the 15,000 new meters after many of the city's 40-year-old meters were decapitated by vandals. The sight of thousands of headless parking meter poles was embarrassing--and they cost the District government hundreds of thousands of dollars a month in lost revenue.

The installation of the new meters, which have no moving parts and feature a digital face that indicates the remaining time, was completed in August. The meters take nickels and dimes as well as quarters and are much tougher to remove from their posts. Even if they are detached from the poles, Lockheed Martin IMS Vice President Donella Brockington said, it is still difficult to get the money out.

The cost of recalibrating the meters to fix the missed-coin problem is being covered by the manufacturer, and about 4,000 of the repairs have already been completed, Brockington said.

The repairs are being made without having to take any meters out of service because Duncan sent 2,000 extra internal mechanisms.

Duncan, which makes about 100,000 meters a year, installed the same kind in Los Angeles and Berkeley, Calif., and both cities have reported the same problems with coins failing to register. Los Angeles Parking Administrator Jim Sherman said a survey conducted during the last two weeks by the city Department of Transportation found that 7 percent of the meters tested were not properly registering coins or had other problems.

Los Angeles officials are so concerned about the matter they are considering giving refunds to motorists who have received tickets after using the meters, while also asking Duncan to make repairs, Sherman said.

Company officials said they are convinced the trouble in the District's meters will be eliminated once the adjustments are made.

"Our optimal goal is you never put money in there without getting time," Tuxen said.

Motorists who find meters that do not register a coin or that have other problems should report the trouble to the Department of Public Works at 202-541-6030, a number that is now being printed on each of the city's meters. Drivers who want a refund are referred to the city's claims division of the corporation counsel's office.

Constance Z. Maravell, who failed to get credit for several coins she dropped into a meter recently on 23th Street NW, said she briefly considered taking revenge.

"I had the very ugly thought that I wanted to lop the head off the meter," she said.

CAPTION: The District installed 15,000 of these new, computerized meters last year.